I have a buddy of mine who wants to reclass back to their old MOS. He feels lost in the MOS that he is in now which is 92A. His old MOS was 42A.

Can he go back to his MOS so he can go warrant as a personnel tech?

Obviously he's not an initial term, but is he within his re-up window? What rank, etc?

Changing a PMOS to a SMOS (and vice versa) is a request (DA Form 4187) through your chain of command and Career Counselor to HRC.

HRC will make a determination based on strengths of both MOS and rank. If the higher priority is 92A, you'll stay a 92A.